A current problem in secondary oil recovery through chemical injection is the need to obtain a representative downhole sample at a specific location. This problem arises from the need for a truly representative sample of produced fluids at a specific wellbore depth. Previous oil well samplers are not capable of accomplishing both of these requirements.
Likewise, very often a true, representative sample of the fluid in a well is desired but not necessarily obtained. A current problem in secondary oil recovery, for example, is the need for a sample of the injected polymer in an injection well at the depth of the intended injection interval. After this polymer has entered the formation and backflowed thereafter, it must be sampled without having its physical properties altered as it is lifted to the surface for analyzing and testing. An additional example is the need to sample polymer which has flowed through the oil bearing formation from the injection well to the producing well. This sample must also be obtained and lifted to the surface without altering its physical properties.
Various problems arise in obtaining the sample of the well fluid. First, the injection well fluid or polymer is stagnant and so the polymer must be made to flow into the sampler. Second, and most importantly, most polymers cannot be subjected to high shear rates which occur during high flow rates. Conventional bottom hole samplers enter the well with the sample chamber at atmospheric pressure and when opened in the wellbore at the formation depth will rapidly fill exposing the sample to very high shear rates. The high shear rates particularly alter the physical properties of the polymer and accordingly produce a nonrepresentative sample. The method and sampler disclosed herein provide a true and representative sample from the perforated interval, for example.
A sampler is desired, but seldom found, that provides a true representative sample of the well fluid at the exact depth desired. And one that ensures that no contaminant such as atmospheric air is introduced into the sample as is common.
Also, a non-pressurized sample is highly desired whereby high fluid pressure build-up is obviated and sudden release of the high fluid pressure on the operator removing the fluid sample from the sampler is prevented. This fluid pressure build-up in the sample chamber as it ascends from deep in the well to the surface is a serious hazard to sampler personnel.